1. Field of the Invention
The present invention relates to semiconductor devices and semiconductor memory devices, and more particularly to a semiconductor device and a semiconductor memory device provided with a function to adjust the internal current setting.
2. Description of the Background Art
Semiconductor devices and semiconductor memory devices often require adjustment of the setting of internal currents such as a leakage current in a standby mode and an operating current for accurate performance of an desired operation. A typical configuration employed is one which evaluates the internal currents in an operation test (test mode) and adjusts the setting of the internal currents by fuse cut or the like, based on the evaluation results.
In particular, it is a critical issue to suppress the leakage current in the standby mode for a semiconductor device and a semiconductor memory device mounted to battery-driven portable equipment, for which there is an increasing demand for lower power consumption.
A configuration for suppressing the leakage current in the standby mode is disclosed, e.g., in Japanese Patent Laying-Open No. 11-339470. Specifically, it discloses a configuration of a dynamic random access memory (DRAM) which permits adjustment of a potential difference between a non-selected level of a word line and a low level of a bit line, such that the leakage current of a MOS transistor for use in address selection in an off state is not to exceed a desired current value.
On the other hand, a magnetic random access memory (MRAM) device and an Ovonic unified memory (OUM) device have recently attracted attention as new types of memory devices.
For example, as disclosed in Roy Scheuerlein et. al, “A 10 ns Read and Write Non-Volatile Memory Array Using a Magnetic Tunnel Junction and FET Switch in each Cell”, 2000 IEEE ISSCC Digest of Technical Papers, TA7.2, an MRAM device performs nonvolatile data storage using a plurality of thin film magnetic elements formed on a semiconductor integrated circuit, permitting random accesses to the respective thin film magnetic elements. In particular, recent announcement shows that performance of the MRAM device is significantly improved by using memory cells (hereinafter, also referred to as “MTJ memory cells”) formed of the thin film magnetic elements utilizing magnetic tunnel junctions (MTJ). The MTJ memory cell stores data as it is magnetized by a magnetic field generated by a data write current, in a direction in accordance with data to be written.
Further, as disclosed in Yasuaki Nagahiro, “Forefront of Non-Volatile Memory—The Future in Intel's Mind: From Flash Memory to “OUM””, Nikkei Microdevices, Nikkei Business Publications, Inc., March 2002, pp. 65-78, a memory cell constituting an OUM device (hereinafter, also referred to as “OUM cell”) is formed with a thin film chalcogenide layer and a power-generating element. Chalcogenide attains an amorphous state or a crystalline state in accordance with a heat pattern from the power-generating element through which a data write current passes. The chalcogenide layer has electric resistances which differ in the amorphous state and in the crystalline state. The OUM cell is supplied with a data write current of one of the two patterns corresponding to the two heat patterns in accordance with data to be written, and attains the amorphous state or the crystalline state to store the data.
In the MRAM device and the OUM device, data write is performed in response to supply of a data write current (internal current). Thus, it is necessary to adjust the setting of the data write current with high precision.
In adjustment of the internal current setting as described above, it is desired that both evaluation of the internal current in a test mode and adjustment of the internal current setting based on the evaluation result can be performed with simple configurations. That is, it is necessary to make the configurations of the evaluation circuit of a leakage current or a data write current in the test mode and the setting adjustment circuit of the same in an actual operation as simple as possible.